Considering the wide potential applicability and the desirability of correcting many cardiovascular lesions in infancy in order to avoid adverse medical, psychological and financial complications, methods to devise growing grafts for vascular and valvular reconstruction will be sought through the present investigation. Growth in thin fascial grafts to the atrium or valves has been noted only rarely. Viability of autologous rectus sheath used for pulmonary artery replacement was demonstrated in our earlier experiments. Increase in size of thoracic grafts was seen in preliminary angiograms in six growing puppies. In this study we propose to investigate the fate of autologous rectus sheath replacement of the aorta in puppies and calves and compare this to aortic autografts and homografts. If positive findings are produced, then we will extend the study to valve replacement by autologous rectus sheath, valve autografts and homografts. Serial measurements, angiograms, microscopic sections and stereology will be performed to determine whether growth or mere stretching occur. Thus, it is hoped that by following theese long-term experiments in puppies and calves, local and systemic factors affecting growth of autologous and homologous tissues used as vascular replacement can be elucidated. Heretofore, no detailed analysis of such factors has been found and there are no "growing grafts" for use in infants.